apoB-containing Lipoproteins Research Articles

Zebrafish are resilient to the loss of major diacylglycerol acyltransferase enzymes

In zebrafish, maternally deposited yolk is the source of nutrients for embryogenesis prior to digestive system maturation. Yolk nutrients are processed and secreted to the growing organism by an extra-embryonic tissue, the yolk syncytial layer (YSL). Export of lipid from the YSL occurs through the production of triacylglycerol-rich lipoproteins. Here we report that mutations in the triacylglycerol synthesis enzyme, diacylglycerol acyltransferase-2 (Dgat2), cause yolk sac opacity due to aberrant accumulation of cytoplasmic lipid droplets in the YSL. Though triacylglycerol synthesis continues, it is not properly coupled to lipoprotein production as dgat2 mutants produce fewer, smaller, ApoB-containing lipoproteins. Unlike DGAT2-null mice, which are lipopenic and die soon after birth, zebrafish dgat2 mutants are viable, fertile and exhibit normal mass and adiposity. Residual Dgat activity cannot be explained by the activity of other known Dgat isoenzymes, as dgat1a;dgat1b;dgat2 triple mutants continue to produce YSL lipid droplets and remain viable as adults. Further, the newly identified diacylglycerol acyltransferase, Tmem68, is also not responsible for the residual triacylglycerol synthesis activity. Unlike overexpression of Dgat1a and Dgat1b, monoacylglycerol acyltransferase-3 (Mogat3b) overexpression does not rescue yolk opacity, suggesting it does not possess Dgat activity in the YSL. However, mogat3b;dgat2 double mutants exhibit increased yolk opacity and often have structural alterations of the yolk extension. Quadruple mogat3b;dgat1a;dgat1b;dgat2 mutants either have severely reduced viability and stunted growth, or do not survive past 3 days post fertilization, depending on the dgat2 mutant allele present. Our study highlights the remarkable ability of vertebrates to synthesize triacylglycerol through multiple biosynthetic pathways.

Remnant cholesterol, not LDL cholesterol, explains peripheral artery disease risk conferred by apolipoprotein B: a cohort study

Abstract Background Elevated apolipoprotein B (apoB)-containing lipoproteins (=remnants + low-density lipoproteins [LDL]) are a major risk factor for atherosclerotic cardiovascular disease, including peripheral artery disease (PAD) and myocardial infarction. We tested the hypothesis that remnants and LDL both explain part of the increased risk of PAD conferred by elevated apoB-containing lipoproteins. For comparison, we also studied risk of chronic limb-threatening ischemia and myocardial infarction. Methods ApoB, remnant cholesterol, and LDL cholesterol were measured in 93,461 individuals without statin use at baseline from the Copenhagen General Population Study (2003-2015). During up to 15 years of follow-up, 1,207 had PAD, 552 had chronic limb threatening ischemia, and 2,022 had myocardial infarction in the national Danish Patient Registry. Remnant and LDL cholesterol were calculated from a standard-lipid profile. Remnant and LDL particle counts were additionally measured with nuclear magnetic resonance spectroscopy in 25,347 of the individuals. Results were replicated in 302,167 individuals without statin use from the UK Biobank (2004-2010). Results In the Copenhagen General Population Study, multivariable adjusted hazard ratios for risk of PAD per 1 mmol/L (39 mg/dL) increment in remnant and LDL cholesterol were 1.9 (95% confidence interval: 1.5-2.4) and 1.1 (1.0-1.2), respectively; corresponding results in the UK Biobank were 1.7 (1.4-2.1) and 0.9 (0.9-1.0), respectively. In the association from elevated apoB to increased risk of PAD, remnant and LDL cholesterol explained 73% (32-100%) and 8% (0-46%), respectively; corresponding results were 63% (30-100%) and 0% (0-33%) for risk of chronic limb-threatening ischemia, and 41% (27-55%) and 54% (38-70%) for risk of myocardial infarction; results for remnant and LDL particle counts corroborated these findings. Conclusions PAD risk conferred by elevated apoB-containing lipoproteins was explained mainly by elevated remnants, while myocardial infarction risk was explained by both elevated remnants and LDL.

Apolipoprotein B gene expression and regulation in relation to Alzheimer’s disease pathophysiology

Apolipoprotein B (APOB), a receptor-binding protein present in cholesterol-rich lipoproteins, has been implicated in Alzheimer's disease (AD). High levels of APOB-containing low-density lipoproteins (LDL) are linked to the pathogenesis of both early-onset familial and late onset sporadic AD. Rare coding mutations in the APOB gene are associated with familial AD, suggesting a role for APOB-bound lipoproteins in the central nervous system.This research explores APOB gene regulation across the AD spectrum using four cohorts: BRAINEAC (elderly control brains), DBCBB (controls, AD brains), ROSMAP (controls, MCI, AD brains), and ADNI (control, MCI, AD clinical subjects). APOB protein levels, measured via mass spectrometry and ELISA, positively correlated with AD pathology indices and cognition, while APOB mRNA levels showed negative correlations. Brain APOB protein levels also correlated with cortical Aβ levels.A common coding variant in the APOB gene locus affected its expression but didn't impact AD risk or brain cholesterol concentrations, except for 24-S-hydroxycholesterol. Polymorphisms in the CYP27A1 gene, notably rs4674344, were associated with APOB protein levels. A negative correlation was observed between brain APOB gene expression and AD biomarker levels. CSF APOB correlated with Tau pathology in presymptomatic subjects, while cortical APOB was strongly associated with cortical Aβ deposition in late-stage AD.The study discusses the potential link between blood-brain barrier dysfunction and AD symptoms in relation to APOB neurobiology. Overall, APOB's involvement in lipoprotein metabolism appears to influence AD pathology across different stages of the disease.

FITM2 deficiency results in ER lipid accumulation, ER stress, and reduced apolipoprotein B lipidation and VLDL triglyceride secretion in vitro and in mouse liver

Triglycerides (TGs) associate with apolipoprotein B100 (apoB100) to form very low density lipoproteins (VLDLs) in the liver. The repertoire of factors that facilitate this association is incompletely understood. FITM2, an integral endoplasmic reticulum (ER) protein, was originally discovered as a factor participating in cytosolic lipid droplet (LD) biogenesis in tissues that do not form VLDL. We hypothesized that in the liver, in addition to promoting cytosolic LD formation, FITM2 would also transfer TG from its site of synthesis in the ER membrane to nascent VLDL particles within the ER lumen. Experiments were conducted using a rat hepatic cell line (McArdle-RH7777, or McA cells), an established model of mammalian lipoprotein metabolism, and mice. FITM2 expression was reduced using siRNA in cells and by liver specific cre-recombinase mediated deletion of the Fitm2 gene in mice. Effects of FITM2 deficiency on VLDL assembly and secretion invitro and invivo were measured by multiple methods, including density gradient ultracentrifugation, chromatography, mass spectrometry, stimulated Raman scattering (SRS) microscopy, sub-cellular fractionation, immunoprecipitation, immunofluorescence, and electron microscopy. 1) FITM2-deficient hepatic cells invitro and invivo secrete TG-depleted VLDL particles, but the number of particles is unchanged compared to controls; 2) FITM2 deficiency in mice on a high fat diet (HFD) results in decreased plasma TG levels. The number of apoB100-containing lipoproteins remains similar, but shift from VLDL to low density lipoprotein (LDL) density; 3) Both invitro and invivo, when TG synthesis is stimulated and FITM2 is deficient, TG accumulates in the ER, and despite its availability this pool is unable to fully lipidate apoB100 particles; 4) FITM2 deficiency disrupts ER morphology and results in ER stress. The results suggest that FITM2 contributes to VLDL lipidation, especially when newly synthesized hepatic TG is in abundance. In addition to its fundamental importance in VLDL assembly, the results also suggest that under dysmetabolic conditions, FITM2 may be an important factor in the partitioning of TG between cytosolic LDs and VLDL particles.

Lipoprotein(a) and risk-weighted apolipoprotein B: a novel metric for atherogenic risk

BackgroundRetention of apolipoprotein B (apoB)-containing lipoproteins within the arterial wall plays a major causal role in atherosclerotic cardiovascular disease (ASCVD). There is a single apoB molecule in all apoB-containing lipoproteins. Therefore, quantitation of apoB directly estimates the number of atherogenic particles in plasma. ApoB is the preferred measurement to refine the estimate of ASCVD risk. Low-density lipoprotein (LDL) particles are by far the most abundant apoB-containing particles. In patients with elevated lipoprotein(a) (Lp(a)), apoB may considerably underestimate risk because Mendelian randomization studies have shown that the atherogenicity of Lp(a) is approximately 7-fold greater than that of LDL on a per apoB particle basis. In subjects with increased Lp(a), the association between LDL-cholesterol and incident CHD (coronary heart disease) is increased, but the association between apoB and incident CHD is diminished or even lost. Thus, there is a need to understand the mechanisms of Lp(a), LDL-cholesterol and apoB-related CHD risk and to provide clinicians with a simple practical tool to address these complex and variable relationships. How can we understand a patient’s overall lipid-driven atherogenic risk? What proportion of this risk does apoB capture? What proportion of this risk do Lp(a) particles carry? To answer these questions, we created a novel metric of atherogenic risk: risk-weighted apolipoprotein B.MethodsIn nmol/L: Risk-weighted apoB = apoB - Lp(a) + Lp(a) x 7 = apoB + Lp(a) x 6. Proportion of risk captured by apoB = apoB divided by risk-weighted apoB. Proportion of risk carried by Lp(a) = Lp(a) × 7 divided by risk-weighted apoB.ResultsRisk-weighted apoB agrees with risk estimation from large epidemiological studies and from several Mendelian randomization studies.ConclusionsApoB considerably underestimates risk in individuals with high Lp(a) levels. The association between apoB and incident CHD is diminished or even lost. These phenomena can be overcome and explained by risk-weighted apoB.

MicroRNA-615-3p decreases apo B expression in human liver cells

Plasma lipids are mainly carried in apolipoprotein B (apoB) containing lipoproteins. High levels of these lipoproteins are associated with several metabolic diseases and lowering their plasma levels is associated with reduced incidence of atherosclerotic cardiovascular disease. MicroRNAs (miRs) are small non-coding RNAs that reduce the protein expression of their target mRNAs and are potential therapeutic agents. Here, we identified a novel miR-615-3p that interacts with human 3′-UTR of apoB mRNA, induces post-transcriptional mRNA degradation, and reduces cellular and secreted apoB100 in human hepatoma Huh-7 cells. Reducing cellular miR-615-3p levels by CRISPR-sgRNA increased cellular and secreted apoB100 indicating endogenous miR regulates apoB expression. Overexpression of miR-615-3p along with or without palmitic acid treatment decreased cellular and media apoB and increased cellular triglyceride levels without inducing endoplasmic reticulum stress. These studies have identified miR-615-3p as a negative regulator of apoB expression in human liver-derived cells. It is likely that there are more miRs that regulate apoB-containing lipoprotein assembly and secretion. Discovery of additional miRs may uncover novel mechanisms that control lipoprotein assembly and secretion.

Apolipoprotein B-48 and late graft failure in kidney transplant recipients.

Transplant vasculopathy resembles atherosclerotic plaque formation and is a major contributor to late graft failure in kidney transplant recipients (KTR). Remnant lipoproteins and associated triglycerides are causal risk factors for atherosclerotic plaques and have been implicated in late kidney graft failure. However, whether remnants derived from liver (containing apolipoprotein [apo] B100) or intestine (containing apoB48) are clinically more important is unclear. The current study investigated the association between baseline fasting apoB48 levels and late kidney graft failure. 481 KTR with a functioning graft for at least 1 year were included in this retrospective, observational longitudinal single center cohort study. The primary endpoint was death-censored late graft failure, defined as need for initiation of dialysis or re-transplantation. ApoB48 was measured by enzyme-linked immunosorbent assay. During a median follow-up of 9.5 years, 61 KTR developed graft failure (12.7%). At baseline, KTR with higher apoB48 levels had lower eGFR (P<.001), lower high-density lipoprotein (HDL) cholesterol (P<.001), increased triglycerides (P<.001) and used cyclosporine more frequently (P=.003). Cox regression showed that higher baseline apoB48 was associated with higher risk of late graft failure [hazard ratio (95% confidence interval), 1.59 (1.22, 2.07), P<.001], independent of stepwise adjustment for potential confounders, including age and sex, immunosuppression type and proteinuria, triglycerides, and waist circumference (fully adjusted HR, 1.78 (1.29, 2.47), P<.001]. ApoB48 is strongly associated with late graft failure, independent of potential confounders. Since apoB48-containing lipoproteins originate from the intestine, this study provides a rationale for considering pharmacological interventions targeting lipid absorption to improve graft outcome.

Biosynthesis and Metabolism of ApoB-Containing Lipoproteins.

Recent advances in human genetics, together with a substantial body of epidemiological, preclinical and clinical trial evidence, strongly support a causal relationship between triglyceride-rich lipoproteins (TRLs) and atherosclerotic cardiovascular disease. Consequently, the secretion and metabolism of TRLs have a significant impact on cardiovascular health. This knowledge underscores the importance of understanding the molecular mechanisms and regulation of very-low-density lipoprotein (VLDL) and chylomicron biogenesis. Fortunately, there has been a resurgence of interest in the intracellular assembly, trafficking, degradation, and secretion of VLDL, leading to many ground-breaking molecular insights. Furthermore, the identification of molecular control mechanisms related to triglyceride metabolism has greatly advanced our understanding of the complex metabolism of TRLs. In this review, we explore recent advances in the assembly, secretion, and metabolism of TRLs. We also discuss available treatment strategies for hypertriglyceridemia.

A suite of genome-engineered hepatocytes empower the identification of novel regulators of APOB and APOB-containing lipoprotein secretion

A suite of genome-engineered hepatocytes empower the identification of novel regulators of APOB and APOB-containing lipoprotein secretion

Fibrinogen and plasma clot properties are associated with apolipoprotein B and apolipoprotein B-containing lipoproteins in Africans

Fibrinogen and plasma clot properties are associated with apolipoprotein B and apolipoprotein B-containing lipoproteins in Africans

A high-cholesterol zebrafish diet promotes hypercholesterolemia and fasting-associated liver steatosis

Zebrafish are an ideal model organism to study lipid metabolism and to elucidate the molecular underpinnings of human lipid-associated disorders. Unlike murine models, to which various standardized high lipid diets such as a high-cholesterol diet (HCD) are available, there has yet to be a uniformly adopted zebrafish HCD protocol. In this study, we have developed an improved HCD protocol and thoroughly tested its impact on zebrafish lipid deposition and lipoprotein regulation in a dose- and time-dependent manner. The diet stability, reproducibility, and fish palatability were also validated. Fish fed HCD developed hypercholesterolemia as indicated by significantly elevated ApoB-containing lipoproteins (ApoB-LPs) and increased plasma levels of cholesterol and cholesterol esters. Feeding of the HCD to larvae for 8 days produced hepatic steatosis that became more stable and sever after 1 day of fasting and was associated with an opaque liver phenotype (dark under transmitted light). Unlike larvae, adult fish fed HCD for 14 days followed by a 3-day fast did not develop a stable fatty liver phenotype, though the fish had higher ApoB-LP levels in plasma and an upregulated lipogenesis gene fasn in adipose tissue. In conclusion, our HCD zebrafish protocol represents an effective and reliable approach for studying the temporal characteristics of the physiological and biochemical responses to high levels of dietary cholesterol and provides insights into the mechanisms that may underlie fatty liver disease.

It is time to address the contribution of cholesterol in all apoB-containing lipoproteins to atherosclerotic cardiovascular disease.

On average, LDL particles are the most populous lipoprotein in serum under fasting conditions. For many reasons, it has been the primary target of lipid-lowering guidelines around the world. In the past 30 years, we have witnessed remarkable changes in each iteration of dyslipidaemia guidelines, with LDL-cholesterol (LDL-C) targets becoming lower and lower among patients at high and very high risk for atherosclerotic cardiovascular disease (ASCVD). The world over, goal attainment rates are low, and hence, ASCVD prevalence remains unacceptably high. Inadequate LDL-C lowering is a major issue in contemporary cardiovascular (CV) medicine. Another issue that vexes even the most astute clinician is that of 'residual risk', meaning the excess risk that remains even after LDL-C is appropriately reduced. In recent years, an important new component of residual risk has emerged: triglyceride-enriched lipoproteins or remnant lipoproteins. These precursors to LDL particles can assume outsized importance among patients with derangements in triglyceride metabolism (e.g. genetic variants, insulin resistance, and diabetes mellitus) and may be more atherogenic than LDL species. Consequently, to reduce total risk for acute CV events, the time has come to include the entire spectrum of apoB-containing lipoproteins in approaches to both risk evaluation and treatment.

Silicon as a Functional Meat Ingredient Improves Jejunal and Hepatic Cholesterol Homeostasis in a Late-Stage Type 2 Diabetes Mellitus Rat Model.

Silicon included in a restructured meat (RM) matrix (Si-RM) as a functional ingredient has been demonstrated to be a potential bioactive antidiabetic compound. However, the jejunal and hepatic molecular mechanisms by which Si-RM exerts its cholesterol-lowering effects remain unclear. Male Wistar rats fed an RM included in a high-saturated-fat high-cholesterol diet (HSFHCD) combined with a low dose of streptozotocin plus nicotinamide injection were used as late-stage type 2 diabetes mellitus (T2DM) model. Si-RM was included into the HSFHCD as a functional food. An early-stage TD2M group fed a high-saturated-fat diet (HSFD) was taken as reference. Si-RM inhibited the hepatic and intestinal microsomal triglyceride transfer protein (MTP) reducing the apoB-containing lipoprotein assembly and cholesterol absorption. Upregulation of liver X receptor (LXRα/β) by Si-RM turned in a higher low-density lipoprotein receptor (LDLr) and ATP-binding cassette transporters (ABCG5/8, ABCA1) promoting jejunal cholesterol efflux and transintestinal cholesterol excretion (TICE), and facilitating partially reverse cholesterol transport (RCT). Si-RM decreased the jejunal absorptive area and improved mucosal barrier integrity. Consequently, plasma triglycerides and cholesterol levels decreased, as well as the formation of atherogenic lipoprotein particles. Si-RM mitigated the dyslipidemia associated with late-stage T2DM by Improving cholesterol homeostasis. Silicon could be used as an effective nutritional approach in diabetic dyslipidemia management.

Effect of body mass index and cholesterol-rich apolipoprotein-B-containing lipoproteins on clinical outcome in NSCLC patients treated with immune checkpoint inhibitors-based therapy: A retrospective analysis.

Obesity and hypercholesterolemia are linked to unfavor clinical outcomes. Recent studies declared the paradox that high body mass index (BMI) and serum cholesterol were independently connected to better clinical outcome of immune checkpoint inhibitors (ICIs) monotherapy in non-small cell lung cancer (NSCLC). The aim of the study is to investigate the prognosis of BMI and serum cholesterol in ICIs-based therapy. This is a retrospective study of 95 NSCLC patients treated with ICIs-based therapy at the Department of Oncology and Lung Cancer Center of China-Japan Friendship Hospital. Treatment efficacy was assessed using durable clinical benefit (DCB) versus nondurable benefit (NDB), best response (active vs. nonactive), and progression-free survival (PFS). The prognostic value of BMI, LDL-C, and RC was determined by multivariate regression analyses, while controlling for confounding factors including age, gender, diabetes status, smoking history, and statin usage. BMI was considered a confounding factor in the analysis when examining the impact of lipoproteins. In our study, we found that in the whole group, BMI ≥25 kg/m2 was linked to a higher risk of poor therapeutic response (OR = 5.92, 95% CI 1.99-19.51, p.val = 0.002) and shorter progression-free survival (HR = 3.00, 95% CI 1.59-5.68, p.val = 0.001). In addition, low levels of RC were associated with better therapeutic response (OR = 0.12, 95% CI 0.02-0.64, p.val = 0.019), while low levels of serum LDL-C were found to predict longer PFS (HR = 0.40, 95% CI 0.19-0.82, p.val = 0.012). These associations were consistent in advanced NSCLC patients receiving ICIs and chemotherapy. Our study suggest that BMI ≥25 kg/m2 and elevated levels of apoB-containing lipoproteins, including LDL-C and RC, could potentially serve as useful prognostic markers for predicting poor treatment outcomes in advanced NSCLC patients treated with the combination of chemotherapy and ICIs.

Metabolic dysfunction-associated steatotic liver disease and atherosclerosis.

To update information about the relationship between metabolic dysfunction-associated steatotic liver disease (MASLD) and atherosclerosis. This review emphasizes the potential mechanisms linking MASLD with atherosclerosis and the possible causal relationships between these conditions. An increased risk of cardiovascular disease is related to MASLD. Several molecular, cellular, and metabolic mechanisms have been described to explain the development of atherothrombosis in MASLD patients. These include atherogenic dyslipidemia, low-grade vascular inflammation, endothelial dysfunction, foam cell formation, proliferation of vascular smooth muscle cells, insulin resistance, gut microbiota dysbiosis, activation of renin-angiotensin and sympathetic nervous systems, hypercoagulability, and decreased fibrinolysis. Also, there is recent evidence suggesting an association between genetically driven liver fat and coronary heart disease mediated by the causal effect of apoB-containing lipoproteins. Several meta-analyses and systematic reviews have reported a strong association between MASLD and cardiovascular outcomes. MASLD is an important and independent risk factor for atherosclerosis development. Multiple mechanisms may be involved in this association. Further research is required to establish a causal association between MASLD and atherosclerosis.

Abstract 115: Scavenger Receptor-BI Mediates Endothelial Uptake Of Lipoprotein(a)

Elevated levels of lipoprotein(a) [Lp(a)], an apoB100-containing lipoprotein, are an independent risk factor for atherosclerotic cardiovascular disease, even in the setting of effective reduction of plasma low-density lipoprotein (LDL) cholesterol. To date, the mechanisms whereby Lp(a) exerts its atherogenic effects remain poorly understood, and no treatments aimed at lowering Lp(a) have been approved. Two receptors - scavenger receptor-BI (SR-BI) and activin receptor-like kinase 1 (ALK1) - have been proposed to bind apoB100 and mediate the atherogenic uptake and transcytosis of LDL across the endothelial cell (EC) barrier. EC-specific SR-BI knockout reduces atherosclerosis in both apoE and LDLR knockout mice. We have shown that SR-BI also mediates EC uptake of nascent chylomicrons. Although binding of ALK1 to apoB is believed to occur through the N-terminus of apoB, the receptor is not involved in the uptake of chylomicrons. We assessed which if any of these receptors are involved in Lp(a) uptake by ECs. Despite the presence of apoB100, EC uptake of Lp(a), like apoB48 chylomicrons, was reduced by SR-BI, but not ALK1, knockdown. We then used a series of small N terminal apoB peptides (apoB3-apoB18, with sequences comprising the 3%, 8%, 12%, 15%, and 18% N terminus of apoB) to compete with Lp(a) uptake. Both chylomicron and Lp(a) uptake was inhibited by apoB15 and apoB18, whereas LDL uptake was additionally inhibited by apoB12. These observations suggest that a) the binding sequence to SR-BI is between residues 547-684 of apoB, and b) an additional sequence between residues 365-547 participates in apoB binding to ALK1. Our findings suggest that apo(a) alters the structure of apoB to make it a better ligand for SR-BI uptake by ECs. Because this uptake pathway leads to transcytosis, we hypothesize that the greater atherogenicity of Lp(a) is mediated by its increased binding to and uptake by ECs.

Abstract 3041: APOB Gene Deletion Increases The Expression Of Vitamin D Binding Protein In Human Hepatoma Cells

High plasma apolipoprotein B (apoB)-containing lipoproteins are both a biomarker and a causal mediator of many metabolic diseases. Inhibition of APOB mRNA decreases plasma lipid levels but at a risk of lipid accumulation in tissues. To understand the global consequences of reduced apoB synthesis, we generated a human hepatoma (Huh-7) cell culture model system deficient in apoB. ApoB deficient Huh-7 cells (Ako) were generated using the CRISPR/Cas9 system. Total RNA for transcriptomics and overnight conditioned media for proteomics and lipidomics was obtained from the Ako and Huh-7 cells (n=3). Statistical analysis was done using Student’s t-test while comparing two groups, p &lt; 0.05 was considered significant. APOB gene deletion significantly reduced APOB mRNA and protein levels in the Ako cells compared to control cells. Ako cells supported apoB48 secretion when transfected with apoB48 expression plasmids. These cells did not accumulate significant amounts of triglyceride. KEGG pathway analysis of RNA-Seq data showed a significant increase in DNA replication/repair pathway and complement/coagulation cascade in the Ako cells. The most downregulated pathways included the PI3k-Akt signaling and MAPK signaling pathways. Differential gene expression analysis identified vitamin D binding protein (VDB, gene GC ) mRNA as the most highly upregulated transcript in Ako cells. The Ako media secretome contained significantly higher amounts of VDB compared to control Huh-7. Furthermore, targeted lipidomics of the secretome showed significant increases in media ergocalciferol. Our qPCR and western blot analysis confirmed increased expression of VDB mRNA and protein secretion in the Ako cells as compared to the Huh-7 cells. We established a cell culture model deficient in secreting apoB-containing lipoproteins. These cells, however, support the assembly and secretion of apoB48 when transfected with apoB48 expression plasmid. A major consequence of apoB deficiency was upregulation of the VDB expression. We interpret these data to suggest that human hepatoma cells have two differentially regulated pathways for the transport of vitamin D. In the absence of apoB-lipoprotein assembly, these cells upregulate VDB to augment secretion of vitamin D.

Abstract 1021: Bulky Hydrophobic Side Chains In The β1-sandwich Of Microsomal Triglyceride Transfer Protein Are Critical For The Transfer Of Both Triglycerides And Phospholipids

Hyperlipidemia predispose individuals to cardio-metabolic diseases, the most common cause of global mortality. Microsomal triglyceride transfer protein (MTP) transfers multiple lipids and is essential for the assembly of apoB-containing lipoproteins. MTP inhibition lowers plasma lipids but causes lipid retention in the liver and intestine. Previous studies suggested two lipid transfer domains in MTP and that specific inhibition of triglycerides (TG) and not phospholipids (PL) transfer can lower plasma lipids without significant tissue lipid accumulation. However, how MTP transfers different lipids and the domains involved in these activities are unknown. Here, we tested a hypothesis that two different β-sandwich domains in MTP transfer TG and PL. Mutagenesis of charged amino acids in β2-sandwich had no effect on PL transfer activity indicating that they are not critical. In contrast, amino acids with bulky hydrophobic side chains in β1-sandwich were critical for both TG and PL transfer activities. Substitutions of these residues with smaller hydrophobic side chains or positive charges reduced, while negatively charged side chains severely attenuated MTP lipid transfer activities. These studies point to a common lipid transfer domain for TG and PL in MTP that is enriched with bulky hydrophobic amino acids. Furthermore, we observed a strong correlation in different MTP mutants with respect to loss of both the lipid transfer activities, again implicating a common binding site for TG and PL in MTP. We propose that targeting of areas other than the identified common lipid transfer domain might reduce plasma lipids without causing cellular lipid retention.

Interactions Between HDL and CD4+ T Cells: A Novel Understanding of HDL Anti-Inflammatory Properties.

Several studies in animal models and human cohorts have recently suggested that HDLs (high-density lipoproteins) not only modulate innate immune responses but also adaptative immune responses, particularly CD4+ T cells. CD4+ T cells are central effectors and regulators of the adaptive immune system, and any alterations in their homeostasis contribute to the pathogenesis of cardiovascular diseases, autoimmunity, and inflammatory diseases. In this review, we focus on how HDLs and their components affect CD4+ T-cell homeostasis by modulating cholesterol efflux, immune synapsis, proliferation, differentiation, oxidative stress, and apoptosis. While the effects of apoB-containing lipoproteins on T cells have been relatively well established, this review focuses specifically on new connections between HDL and CD4+ T cells. We present a model where HDL may modulate T cells through both direct and indirect mechanisms.

Remnant Cholesterol, Not LDL Cholesterol, Explains Peripheral Artery Disease Risk Conferred by apoB: A Cohort Study.

Elevated apoB-containing lipoproteins (=remnants+LDLs [low-density lipoproteins]) are a major risk factor for atherosclerotic cardiovascular disease, including peripheral artery disease (PAD) and myocardial infarction. We tested the hypothesis that remnants and LDL both explain part of the increased risk of PAD conferred by elevated apoB-containing lipoproteins. For comparison, we also studied the risk of chronic limb-threatening ischemia and myocardial infarction. apoB, remnant cholesterol, and LDL cholesterol were measured in 93 461 individuals without statin use at baseline from the Copenhagen General Population Study (2003-2015). During up to 15 years of follow-up, 1207 had PAD, 552 had chronic limb-threatening ischemia, and 2022 had myocardial infarction in the Danish National Patient Registry. Remnant and LDL cholesterol were calculated from a standard lipid profile. Remnant and LDL particle counts were additionally measured with nuclear magnetic resonance spectroscopy in 25 347 of the individuals. Results were replicated in 302 167 individuals without statin use from the UK Biobank (2004-2010). In the Copenhagen General Population Study, multivariable adjusted hazard ratios for risk of PAD per 1 mmol/L (39 mg/dL) increment in remnant and LDL cholesterol were 1.9 (95% CI, 1.5-2.4) and 1.1 (95% CI, 1.0-1.2), respectively; corresponding results in the UK Biobank were 1.7 (95% CI, 1.4-2.1) and 0.9 (95% CI, 0.9-1.0), respectively. In the association from elevated apoB to increased risk of PAD, remnant and LDL cholesterol explained 73% (32%-100%) and 8% (0%-46%), respectively; corresponding results were 63% (30%-100%) and 0% (0%-33%) for risk of chronic limb-threatening ischemia and 41% (27%-55%) and 54% (38%-70%) for risk of myocardial infarction; results for remnant and LDL particle counts corroborated these findings. PAD risk conferred by elevated apoB-containing lipoproteins was explained mainly by elevated remnants, while myocardial infarction risk was explained by both elevated remnants and LDL.